why does this bother me??? how do I let it go???

so basically
I’m like obsessed with Billie Eilish and I always play her songs around the house. The thing is my cousin would get annoyed and hateful. He’d be like if you play Billie I’ll go to my room and stay there. Also I was like I’ll record you a song and he said he doesn’t want to see that.

Now he suddenly obsessed with MY favourite song from her and suddenly wants me to record one of her songs.

I know I don’t own her but it annoys me that he suddenly likes her now. Like honestly I just want to let it go but it irks me deeply.